Note: Descriptions are shown in the official language in which they were submitted.
CA 02460793 2006-11-01
[0001] OUTER LOOP TRANSM[T POWER CONTROL
USING CHANNEL-ADAPTIVE PROCESSING
[0002] BACKGROUND
[0003] The present invention relates to spread spectrum time division duplex
(TDD) communication systems. More particularly, the present invention relates
to a
system and method for controlling outer loop transmission power within TDD
communication systems.
[0004] Spread spectrum TDD systems carry multiple communications over the
same spectrum. The multiple signals are distinguished by their respective chip
code
sequences (codes). Referring to Figure 1, TDD systems use repeating frames 34
divided into a number of time slots 37,-37.,, such as fifteen time slots. In
such
systems, a communication is sent in a selected time slot out of the plurality
of time
slots 37,-37, using selected codes. Accordingly, one frame 34 is capable of
carrying
multiple communications distinguished by both time slot and code. The
combination
of a single code in a single time slot is referred to as a physical channel.
Based on the
bandwidth required to support a communication, one or multiple physical
channels are
assigned to that communication.
[0005] Most TDD systems adaptively control transmission power levels. In a
TDD system, many communications may share the same time slot and spectrum.
While a user equipment (UE) is receiving a downlink transmission from a base
station, all the other communications using the same time slot and spectrum
cause
interference to the specific communication. Increasing the transmission power
level of
one communication degrades the signal quality of all other communications
within that
time slot and spectrum. However, reducing the transmission power level too far
results
in undesirable signal to noise ratios (SNRs) and bit error rates (BERs) at the
receivers.
To maintain both the signal quality of communications and low transmission
power
levels, transmission power control is used.
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[0006] The purpose of power control is to use the minimum power required to
allow each transport channel (TrCH) to operate with the Block Error Rate
(BLER) no
higher than its required level. The standard approach to TDD downlink power
control
is a combination of inner and outer loop control. In this standard solution,
the UE
transmits physical layer transmit power control (TPC) commands to adjust the
base
station transmission power.
[0007] A base station sends a transmission to a particular UE. Upon receipt,
the
UE measures the signal interference ratio (SIR) in all time slots and compares
this
measured value to a targetSIR. This target SIR is generated from the BLER
signaled
from the base station. As a result of a comparison between the measured SIR
value
with the target SIR the UE transmits a TPC command to the base station. The
standard
approach provides for a TPC command per coded composite transport channel
(CCTrCH). The CCTrCH is a physical channel which comprises the combined units
of data for transmission over the radio interface to and from the UE or base
station.
This TPC command indicates to the base station to adjust the transmission
power level
of the downlink communication. The base station, which is set at an initial
transmission power level, receives the TPC command and adjusts the transmit
power
level in all time slots associated with the CCTrCH in unison. The inner loop
power
control algorithm controls transmit power to maintain the received SIR as
close as
possible to a target SIR by monitoring the SIR measurements of the data. The
outer
loop power control algorithm controls the target SIR to maintain the received
quality
BLER as close as possible to a target quality BLER based on the Cyclic
Redundancy
Code (CRC) check of the data. The output from the outer loop power control is
a new
target SIR per CCTrCH used for the inner loop power control.
[0008] There are four main error sources in transmission power control: 1)
channel error; 2) systematic error; 3) random measurement error; and 4) coded
composite transport channel (CCTrCH) processing error. The systematic error
and the
random measurement error are corrected reasonably by the inner loop power
control by
monitoring the SIR measurements. The CCTrCH processing error is corrected by
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either the outer loop power control or the inner loop power control by using
relative SIR
measurements among the codes. The channel error is related to unknown time-
varying
channel conditions.
In power control systems, the outer loop power control algorithm would set a
target
SIR for each CCTrCH based on the required target BLER, assuming a most
plausible
channel condition. Therefore, the mismatch between the target BLER and the
mapped target
SIR varies depending on the actual channel condition, and it is especially
large at very low
BLER. Since the outer loop power control depends on the CRC check, it often
takes a long
time to converge to the required target SIR for the low BLER.
Accordingly, there is a need for outer loop power control which determines the
actual
channel conditions so that a proper value for the target SIR is used.
SUMMARY
The present invention is a system and method which controls outer loop
transmit
power for transmission power of an uplink/downlink communication in a spread
spectrum
time division communication. The system receives a communication from a base
station and
determines an error rate on the received communication. The system then
distinguishes
between static and dynamic channels, produces a static adjustment value, and
characterizes
the dynamic channels to generate a dynamic adjustment value. The target power
level is
then adjusted by the static and dynamic adjustment values, setting the
transmission power
level.
The invention provides according to an aspect for a method for controlling
outer loop
transmit power for transmission power control of an uplink/downlink
communication in a
spread spectrum time division communication system where a user equipment (UE)
pro-
duces a target power level based upon received signals which it communicates
to a base
station from which the signals are received. The method comprises the steps
of: receiving at
the UE a communication in the form of a series of communication segments from
a base
station; analyzing the received communication within first and second
composite windows;
the first composite window having a predefined first window of a first length
of a predeter-
mined number of communication segments and a non-overlapping second window of
a
second length of a predetermined number of communication segments, such that
each seg-
ment of the communication is first analyzed in the first window and
subsequently analyzed
in the second window; the second composite window having a predefined third
window of a
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third length of a predetermined number of communication segments and a non-
overlapping
fourth window of a fourth length of a predetermined number of communication
segments,
such that each segment of the communication is first analyzed in the third
window and sub-
sequently analyzed in the fourth window; periodically distinguishing between
static and
dynamic channel conditions in communication segments within the first and
second
windows; generating a static adjustment value when the respective channel
conditions of the
communication segments in the first and second windows are different;
periodically charact-
erizing dynamic channel conditions in communication segments within the third
and fourth
windows to generate a dynamic adjustment value; and adjusting the target power
level in
response to the static and dynamic adjustment values.
According to another aspect, the invention provides for a receiver in a spread
spec-
trum time division communication system where a user equipment (UE) produces a
target
power level based upon received signals which it communicates to a base
station from which
the signals are received, which controls outer loop transmit power for
transmission power
control of an uplink/downlink communication and receives a communication in
the form of a
series of communication segments from a base station, comprising a processor
for generating
the target power level which is communicated to the base station and analyzing
the received
communication within first and second composite windows; the first composite
window,
having a predefined first window of a first length of a predetermined number
of communica-
tion segments and a non-overlapping second window of a second length of a
predetermined
number of communication segments, such that each segment of the communication
is first
analyzed in the first window and subsequently analyzed in the second window,
for periodic-
ally distinguishing between static and dynamic channel conditions in
communication seg-
ments within the first and second windows and generating a static adjustment
value when the
respective channel conditions of the communication segments in the first and
second
windows are different; the second composite window, having a predefined third
window of a
third length of a predetermined number of communication segments and a non-
overlapping
fourth window of a fourth length of a predetermined number of communication
segments,
such that each segment of the communication is first analyzed in the third
window and sub-
sequently analyzed in the fourth window, for periodically characterizing
dynamic channel
conditions in communication segments within the third and fourth windows to
generate a
dynamic adjustment value; the processor adjusting the target power level in
response to the
static and dynamic adjustment values.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates time slots in repeating frames of a TDD system.
Figure 2 illustrates a simplified wireless TDD system.
Figures 3A and 3B illustrate block diagrams of a UE and base station,
respectively.
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[00017] Figure 4 is a graphical illustration of the mapping of the BLER with a
target SIR value.
[00018] Figure 5 is an illustration of the jump algorithm in accordance with
the
present invention.
[00019] Figures 6A and 6B are block diagrams of the split sliding windows for
the first and second filter processes.
[00020] Figure 7 is a flow diagram of channel discrimination filtering for use
in
downlink power control.
[00021] Figure 8 is a flow diagram of fading channel filtering for use in
downlink
power control.
[00022] Figure 9 is a flow diagram of a channel-adaptive downlink outer-loop
power control algorithm of the present invention.
[00023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[00024] The preferred embodiments will be described with reference to the
drawing figures where like numerals represent like elements throughout.
[00025] Figure 2 illustrates a simplified wireless spread spectrum code
division
multiple access (CDMA) or time division duplex (TDD) communication system 18.
The system 18 comprises a plurality of node Bs 26, 32, 34, a plurality of
radio network
controllers (RNC), 36, 38, 40, a plurality of user equipments (UEs) 20, 22, 24
and a
core network 46. The plurality of node Bs 26, 32, 34 are connected to a
plurality
RNCs 36, 38, 40, which are, in turn, connected to the core network 46. Each
Node B,
such as Node B 26, communicates with its associated UEs 20-24. The Node B 26
has
a single site controller (SC) associated with either a single base station 30,
or multiple
base stations 30,...30~.
[00026] Although the present invention is intended to work with one or more
UEs, Node Bs and RNCs, for simplicity of explanation, reference will be made
hereinafter to the operation of a single UE in conjunction with its associated
Node B
and RNC.
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Referring to Figure 3A, the UE 22 comprises an antenna 78, an isolator or
switch 66,
a modulator 64, a demodulator 68, a channel estimation device 70, data
estimation device 72,
a transmit power calculation device 76, an interference measurement device 74,
an error
detection device 112, a processor 111, a target adjustment generator 114, a
reference channel
data generator 56, a data generator 50, and two spreading and training
sequence insertion
devices 52, 58.
The UE 22 receives various radio frequency (RF) signals including
communications
from the base station 30 over the wireless radio channel using an antenna 78,
or alternatively
an antenna array. The received signals are passed through a transmit/receive
(T/R) switch 66
to a demodulator 68 to produce a baseband signal. The baseband signal is
processed, such as
by a channel estimation device 70 and a data estimation device 72, in the time
slots and with
the appropriate codes assigned to the UE's 22 communication. The channel
estimation
device 70 commonly uses the training sequence component in the baseband signal
to provide
channel information, such as channel impulse responses. The channel
information is used by
the data estimation device 72, the interference measurement device 74 and the
transmit
power calculation device 76. The data estimation device 72 recovers data from
the channel
by estimating soft symbols using the channel information.
Prior to transmission of the communication from the base station 301, the data
signal
of the communication is error encoded using an error detection/correction
encoder 110. The
error encoding scheme is typically a CRC followed by a forward error
correction encoding,
although other types of error encoding schemes may be used. As those skilled
in the art
know, the data is typically interleaved over all of the time slots and all
codes.
In accordance with the preferred embodiment of the present invention, downlink
outer loop power control is conducted using a channel adaptive downlink outer
loop power
control, described hereafter. Using the soft symbols produced by the data
estimation device
72, the error detection device 112 detects the target BLER sent from the base
station 301.
Given the target BLER, an initial target SIRTarget is generated
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by mapping the target BLER, using an assumed plausible channel condition, to a
SIR
value associated with the channel condition. A graphical example of this
mapping is
illustrated in Figure 4. The lines on this graph are exemplary propagation
conditions,
wherein the AWGN channel is the static channel for additive white Gaussian
noise,
and case 1 through case 4 are fading channels with different multipaths.
[00031] As shown in Figure 4, at a required BLER, for example 0.01 for a case
1
fading channel, a predetermined transmission power can be determined. In the
above
example, the transmission power is approximately 4.5dB, from which a target
SIR is
calculated. It is also shown in Figure 4 that the SIRT,,,ge, at BLER of 0.01
for the case 1
fading channel requires more than 5dB over the SIRT,et for the case 2 fading
channel.
Accordingly, it will take longer to converge to the required SIRTar?et for a
low BLER
when assuming the case 1 fading channel and trying to get to the SIR,.arge1
for a case 2
fading channel.
[00032] In order to get from the SIR for the case 1 channel, the assumed
channel,
for example, to the required SIR for the case 2 channel, the actual channel
for example,
a jump algorithm is utilized by the processor 111. Initially, the parameters
of the jump
algorithm SIR step_down, SIR step_up are determined using the target BLER in
accordance with the following equations:
SIR step_down = SIR step_size * target BLER Equation 1
SIR step_up = SIR_step_size - SIR step_down; Equation 2
where SIR step_size is any predetermined value, preferably a value between 0.3
dB
and 0.5 dB. As the error detection device 112 detects an error in a
Transmission Time
Interval (TTI), a SIRTarget value is updated by the processor 111 in
accordance with
Equation 3:
SIRTarget (K) = SIRTarget (K-1) + SIR step_up (dB) Equation 3
where K is the number of the TTI. If the error detection device 112 does not
detect an
error in the TTI, the SIRT.ge, is updated in accordance with Equation 4:
SIRTarget (K) = SIRTarget (K-1) - SIR step_down (dB) Equation 4
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[00033] Also, each time a determination is made by the error detector device
112
whether an error is present in a TTI, a step_up counter or step_down counter
is
incremented; the step_up counter being incremented each time an error is
detected; the
step_down counter being incremented otherwise. A graphical representation of
the
jump algorithm used by the processor 111 to set a target SIR is illustrated in
Figure 5.
Again, Figure 5 illustrates that for communications where the assumed channel
condition differs greatly from the actual channel condition, the convergence
from an
assumed target SIR to an actual SIR may take a long time.
[00034] Accordingly, the processor 111 then conducts a channel-adaptive
filtering process to further adjust the SIRTarse,. The channel adaptive
filtering process
includes two (2) filter processes. The first filter process distinguishes the
static and
dynamic (or fading) channels, and the second filter process characterizes the
dynamic
channel conditions. These filter processes are conducted sequentially, (i.e.
the second
after the first), with one another to produce the necessary adjustments to the
SIRT,e, in
accordance with actual channel conditions.
[00035] Both of the filter processes perform their respective filter
processing
using a split sliding window 600, 610. Diagrams of the split sliding windows
600, 610
are shown in Figures 6A and 6B, respectively. The split sliding windows 600,
610
comprise a left side window (LW), a variable gap (GW) and a right side window
(RW). Each of the respective windows may be any length in size; the length
representing the number of values, observations Oõ OZ, to be determined for
each of
respective windows LW, RW. GW represents a transition period of channel
conditions,
which improves the detection of changing channel conditions. For example, if
the left
side window LW was set to a length of 2, the LW would comprise two
observations of
the respective sliding windows 600, 610.
[00036] Each of the respective sliding windows 600, 610 observations' Oõ OZ
are
generated each observation period OPõ OPZ being any number of time segments
within
the received communication. For example, the first filter process sliding
window 600
may have an observation period OP1 of 100 ms, where one (1) time segment
equals 10
ms. Accordingly, one observation O, is made every ten (10) time segments. This
is
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the case for the second filter process sliding window 610 as well. It should
be noted,
though, that the observation periods OPõ OPZ of the filter processes may be
different.
The sliding window moves one step forward per observation period OP1, OP, and
the
each of the filtering processes discriminates channel conditions between RW
and LW.
The values observed/measured Oõ OZ within RW and LW are utilized by the
filtering
processes to generate a SIR adjustment value.
[00037] The algorithm characterizes the channel condition based on the power
of
the strongest path (Po) for static/dynamic channel detection in the first
filter process and
the power ratio of P1/Po (dB) for fading channels, where P, is the power of
the second
strongest path. Po is sampled once per observation period OP1 for the first
filter process
and Pt/Po (dB), for the second filter process, are averaged once per
observation period
OPZ for the second filter process. Each observation Oõ OZ is stored in the
memory to
perform filtering by the split sliding windows 600, 610.
[00038] As stated, the first filtering process 700 distinguishes the static
(i.e., path
of line of sight) and dynamic channels (i.e. fading multipath), determining
whether
there is a transition between a dynamic channel and a static channel. Figure 7
is a flow
diagram of the first filtering process 700 in accordance with the preferred
embodiment
of the present invention. The distinguishing of the static and dynamic
channels is
conducted using the detected peak power of a predetermined observation period
OP,.
[00039] As explained above, the first filtering process utilizes the split
sliding
window, as shown in Figure 6A, to generate a static adjustment value. Again,
the LW
and RW can be of any predetermined length. The GW initially is set to one (1)
(Step
702) and is increased by one (1) each iteration, to be disclosed hereinafter.
The GW,
though, has a preset limitation as to how big it can be, for example, 2 or 3.
[00040] The processor 111 utilizes the step_up and step_down counts generated
in the aforementioned jump algorithm, as well as, the determined power(s) of
the
strongest path in the LW and RW to calculate the static adjustment value. The
first
filter process is run after the LW and the RW are filled in with
observed/measured
peak powers. Accordingly, if the sliding window size was 7, (RW equal 3, LW
equals
3 and GW equals 1), 7 observations O, would have to be observed before the
first filter
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process generates a static adjustment value.
[00041] The static adjustment value is calculated in accordance with the
following. The mean of the peak values of each observation in the LW and RW
and
the A mean of the peak values are calculated (Step 703) in accordance with
Equations
5, 6 and 7 below:
mean_ peak,~w = 1~ Po (i) Equation 5
RW
N
mean_ peakLW = 1 EPo (i) Equation 6
LW ;_Rw+cw+l
A mean_ peak = mean_ peakRW - mean_ peakLW Equation 7
[00042] Once the A mean peak value has been calculated, a threshold test is
conducted (Step 704) to determine whether there is a fluctuation among peak
powers
within each window (LW and RW) and whether there is a change between the RW
and
LW windows, meaning a change from static to dynamic or dynamic to static
channels
within the sliding window. The threshold value is a predetermined value,
preferably:
TH,õean-pepk = 3.0
TH_ Peak.,,a,Rw = 1.0
TH_ Peak.,;a.LW = 1.0
Th_ Peakõd kW and TH_ Peaks,d,LW are thresholds which are related to the
standard
deviation (std) to detect a fluctuation of peak powers for fading channels.
The
threshold test compares the A mean peak values to the threshold and the peak
values of
the RW and LW to determine if there is a transition, meaning the channel
within the
LW is different than the channel within the RW, to determine if the channel
within the
LW is a static channel when the channel within the RW is a fading channel, and
vice
versa.
[00043] If the LW and RW channels are different and either one is static, the
processor 111 sets the jump value SIR,.mP based on the step_up and step_down
counts
of the jump process and computes the initial value of the target SIR static
adjustment
(adjStaticSIRdB) based on the delta mean and BLER (Step 705).
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[00044] The jump value is set according to Equation 8a.
SIRJõmp = SIR_ step_ up * step_ up_ count - SIR_ step_ down * step_ down_
count Equation 8a
The initial value of adjStaticSIRdB, which is an adjustment value relative to
an
assumed reference dynamic channel, (preferably case 2), is set according to
Equation
8b; where the BLER is mapped using the graphs shown Figure 4.
adjStaticSIRdB = -1.5 * Amean peak * log10(1.0/BLER) Equation 8b
[00045] The initial value of adjStaticSIRdB is then modified based on the
power
ratio, depending on whether the RW channel is static or the LW channel that is
static.
If the RW channel is the static channel (and the LW channel is the fading
channel), the
adj StaticSIRdB is modified with the average power ratio of the LW
(AvPrevChChar)
according to the pseudo code and Equation 9 set forth below:
AvPrevChChar = 0;
forj = 1:sizeojLW
AvPrevChChar = AvPrevChChar + prevChChar(l, j + sizeojRW + maxsizeofGap - 1)
end
AvPrevChChar = AvPrevChChar / sizeofLW;
deltaMean = AvPrevChChar + 10.8;
adjStaticSlRdB = adjStaticSlRdB + 0.4 * deltaMean * log10(1.0 / BLER).
Equation 9
If the LW channel is the static channel (and the RW channel is the fading
channel), the
adjusted static SIR adjStaticSIRdB is calculated according to Equation 10:
adjStaticSlRdB = adjStaticSlRdB - 0.4* delta mean* log 10(1.0 / BLER) Equation
10
where delta mean = 7Ø
[00046] Once the initial static adjustment is re-calculated, a determination
is
made as to whether the adjustment is too large, which protects against making
large
adjustments at one time. This is accomplished by comparing the static
adjustment to a
maximum adjustment maxadjSIRdB, where
max adjSlRdB = 3* log 10(1 / BLER). Equation 11
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If the maximum is less than the calculated adjustment, the maximum value is
utilized
as the static adjustment. The processor 111 then adjusts the static adjustment
in
accordance with Equation 12:
adjStaticSlRdB = adjStaticSlRdB - SlRjump Equation 12
[00047] Upon the calculation of the static adjustment, the processor 111
initializes the peak power, step_up and step_down counts, and power ratio for
the new
channel (Step 706). The initialization of the power ratio will set the
reference channel
to the case 2 assumed reference channel used in Equation 8b, to begin the
second filter
process. The initialization of the step_up and step_down counts will set
Equation 8a to
zero in the second filter process so that the SIR~.mP adjustment is not used
twice.
[00048] If the threshold test is not passed (i.e., a change between the RW and
LW
windows is not detected) and the gap size is less than the maximum gap size,
the
processor 111 increases the gap size by one (1) (Step 708) and the peak values
of the
LW and RW and A mean are recalculated (Step 703). If the GW is at the
predetermined maximum, the processor 111 moves the sliding window and begins
the
next observation period OP1 (Step 707).
[00049] As stated above, the processor 111 sequentially conducts the second
filter
process 800 to generate a dynamic (fading) channel adjustment. The second
filter
process 800 characterizes fading channel conditions by using a power ratio of
multipaths. The flow diagram of the second filtering process 800 is
illustrated in
Figure 8. When the first filter process 700 is initially run, the values in
the LW and
RW of the first filter are accumulated by the observed/measured peak powers,
while
the values in the LW of the second filter process 800 are predetermined by the
power
ratios of the assumed plausible channel condition, for example case 1, and the
values in
the GW and RW of the second filter process 800 are accumulated by the
observed/measured power ratios. Once the RW has accumulated an observations OZ
worth of data, the power ratio within that observation OZ is determined. Those
predetermined power ratio values within the LW and any second or third
observed/measured value within RW are used by the processor 111 to determine
the
adjustment value.
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[00050] Similar to the first filter process 700, the second filter process 800
computes the mean difference of the LW and RW power ratio values computed in
each. As stated earlier, the sliding window for the second filter process 800
comprises
a LW, RW and GW, which can be of any predetermined length (Step 803). The
power
ratio for each observation in each window is computed according to Equation 13
below:
Nom
Pio (t) = Nobs E 10 *[log 10(P, (j)) - log 10(Po (j))] Equation 13
where Nobs is the number of samples per observation period OPZ, Po(j) is the
power of
the strongest path and P1(j) is the power of the second strongest path.
[00051] The mean power ratios and the delta mean (Amean) are then calculated
in
accordance with equations 14, 15 and 16 below:
1 RW
meanRW = RW I P,o (i) Equation 14
,-,
N
meanLW = LW I RwE P,o (i) Equation 15
A mean = meanRw - mean, w Equation 16
[00052] Similar to the first filter process 700, threshold values are
generated and
the mean and power ratios of the RW and LW are compared to the threshold (Step
804). The threshold values are computed in accordance with the following
pseudo-
code:
if ((meanLw > -7.0)& (meanRw > -7.0))
THmean = 2.0;
THr,d,,,w = abs(0.35 * 0 mean);
THs,d,Rw = abs(0.5 * A mean);
else
THmean = 3.0;
THs,d, w= abs(0.3 * A mean);
THs,d,Rw = abs(0.5 * 0.3 * 0 mean);
End
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where -7.0 represents the fading channel conditions that have weak second path
or no
second path.
[00053] If the mean difference and the power ratio values of the RW and LW
are within the threshold range, the processor 111 sets the SIR,-', and an
initial
fading channel SIR adjustment (Step 805) according to Equations 17 and 18,
below:
SIRi,,,,,p = SIR_ step_ up * step_ up_ count - SIR step_ down * step_ down
count Equation 17
SIR, ~se1 = a * A mean * log 10(1 / BLER) Equation 18
where the BLER is again mapped from the assumed reference channel.
[00054] If the initial SIRt az''' g et is greater than a maximum adjustment,
max adjSlRdB = 3 * log 10(l / BLER) Equation 19
then the SIR;~~e1 is set to maxadjSIRdB. The processor 111 then adjusts the
initial or
maximum adjustmentSIR, ~~e! by SIR~ump=
SIR; 'ge~ = SIR, a'ge1- SIRj,,,,,p Equation 20
The SIRt az'''get presents a fading channel adjustment to the assumed
reference channel. For
example, if the assumed reference channel is case 2 and the actual channel
condition is
a case 3 channel, the SIR, ~set adjusts the static adjustment generated by the
first filter
process 700 to reduce or increase the static adjustment value so that the
target SIR sent
to the base station represents actual channel conditions of the case 3
channel.
[00055] If the threshold test is not passed, the second filter process
operates
similar to the first filter process in that the gap size is incremented by one
(1) (Step
808) if it is not greater than or equal to the maximum gap size, or the
sliding window
moves by one step forward for the next observation period (Step 807) and the
SIR ~ se1
is set to 0.
[00056] Each time an observation is completed for the first and/or second
filter
process, the SIRT,get is determined according to Equation 21, below:
t arg et_ SIR(k) = t arg et_ SIR(k - 1) + adjstaticSlRdB + SIR, ars e,
Equation 21
[00057] The processor 111 determines the adjustment of the base station
transmit
power by comparing the measured SIR with the SIRTarget = Using this
comparison, a
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TPC command is subsequently sent to the base station 80.
[00058] Referring to Figure 3B, the base station 80 comprises, an antenna 82,
an
isolator or switch 84, a demodulator 86, a channel estimation device 88, a
data
estimation device 90, processor 103, a transmission power calculation device
98, a data
generator 102, an encoder 110, an insertion device 104 and a modulator 106.
The
antenna 82 or, alternately, antenna array of the base station 301 receives
various RF
signals including the TPC command. The received signals are passed via a
switch 84
to a demodulator 86 to produce a baseband signal. Alternatively separate
antennas
may be used for transmit or receive functions. The baseband signal is
processed, such
as by a channel estimation device 88 and a data estimation device 90, in the
time slots
and with the appropriate codes assigned to the communication burst of the UE
22. The
channel estimation device 88 uses the training sequence component in the
baseband
signal to provide channel information, such as channel impulse responses. The
channel information is used by the data estimation device 90. The data
information is
provided to the transmit power calculation device 98 by processor 103.
[00059] Processor 103 converts the soft symbols produced by the data
estimation
device 90 to bits and extracts the TPC command associated with the CCTrCH. The
transmit power calculation device 98 increases or decreases the transmission
power for
the CCTrCH by the predetermined step size according to the TPC command.
[00060] Data to be transmitted from the base station 30, is produced by data
generator 102. The data is error detection/correction encoded by error
detection/correction encoder 110. The error encoded data is spread and time-
multiplexed with a training sequence by the training sequence insertion device
104 in
the appropriate time slot(s) and code(s) of the assigned physical channels,
producing a
communication burst(s). The spread signal is amplified by an amplifier 106 and
modulated by modulator 108 to radio frequency. The gain of the amplifier is
controlled by the transmit power calculation device 98 to achieve the
determined
transmission power level for each time slot. The power controlled
communication
burst(s) is passed through the isolator 84 and radiated by the antenna 82.
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[00061] The flow diagram of the channel-adaptive downlink outer-loop power
control algorithm of the present invention is illustrated in Figure 9. A
target BLER is
communicated to the receiver 10 from the base station 30, (Step 901). Using
the
received target BLER, a target SIR is obtained for a given channel (Step 902)
and the
step_up and step_down sizes for the jump algorithm are calculated (Step 903).
The
step_up and step_down counters are initialized and the parameters for the
first and
second filter processes are set (i.e., observation periods) (Step 904).
[00062] If the receiver 10 is synchronized with the base station and there is
no
discontinuation of transmission (DTX), the jump algorithm is conducted by the
processor 111 (Step 905). Upon the generation of the SIRTar,,e, by the jump
algorithm,
the processor 111 conducts the first filter process (Step 906) to generate a
static
adjustment value. Once the first filter process has accumulated enough
observations to
fill the first sliding window, the process calculates the peak power (Step
907) and
generates the static SIR adjustment (Step 908). The processor 111 then
conducts the
second filter process (step 909). The power ratios are calculated for each
observation
OZ within the second filter window (step 910) and generates the fading channel
adjustment (Step 911). The SIRTazget is then adjusted according to the
adjustment values
generated by the first and second filter processes respectively 700, 800 (Step
912).
[00063] The downlink outer loop power control algorithm, in accordance with
the
preferred embodiment of the present invention utilizes ajump algorithm and a
channel-
adaptive algorithm to mitigate the channel error and adapts to the time-
varying channel
conditions. If the channel-adaptive algorithm uses more samples of P0 and
Pl/P0 per
frame or uses PCCPCH of SCH prior to the TPC, it could shorten the convergence
time. Hence the channel-adaptive outer-loop power control algorithm will meet
the
desirable convergence time and reduce the battery power consumption in the
uplink
TPC and interference in the downlink TPC (results in more capacity). The
channel-
adaptive algorithm can be extended by adding more features, P2/PO, P3/PO, the
number
of multi-paths, etc. to improve performance. Since the algorithm is general,
it can be
applied to the uplink TPC of TDD and the uplink/downlink TPC of FDD.
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[00064] While the present invention has been described in terms of the
preferred
embodiment, other variations which are within the scope of the invention as
outlined in
the claims below will be apparent to those skilled in the art.
* * *
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